The present invention relates generally to accumulators for fluid pressure operated devices and systems.
Accumulators are well-known for storing excess fluid under pressure within a fluid system. Two accumulators which are widely used in the industry are bladder-type accumulators and piston-type accumulators. In the bladder-type accumulator, an elastic bladder is fluidly-sealed at its opening to a fluid tube or to the walls of a canister, and expands and contracts within the canister depending on the volume of fluid entering one end of the canister. Examples of such bladder-type accumulators are shown in U.S. Pat. Nos. 3,408,731 and 4,448,217. The resiliency of the bladder, sometimes in conjunction with a volume of gas surrounding the bladder, tends to urge the bladder into a collapsed or uncharged/exhausted state in the canister.
In a piston-type accumulator, a piston is moveably positioned within an elongated canister, and slides axially depending on the volume of fluid entering one end of the canister. One or more annular seals are provided around the periphery of the piston to maintain a fluid seal with the walls of the housing, and a resistance device, such as a spring, cushion or volume of gas, is provided against the side of the piston opposite from the inlet to urge the piston toward the inlet into an uncharged/exhausted position. Examples of such piston-type accumulators are shown in U.S. Pat. Nos. 2,748,801, 3,757,523 and 3,837,354.
The choice between a piston or bladder depends on the particular application, which should be well-known to those skilled in the art.
In many bladder and piston-type accumulators, a plug or end cap is provided at one or both ends of the accumulator housing. Since the housing must withstand significant pressures, many techniques have been developed in an attempt to create a firm and fluid-tight attachment of each end cap to the housing. Techniques such as bending or rolling over an end of the casing, or threadably attaching an end cap to the canister are known (see, e.g., U.S. Pat. No. 2,748,801 FIGS. 1 and 2). It is also known to create a raised bead or flange surrounding the periphery of the end cap, and then crimping or staking the housing over the bead, as described in U.S. Pat. Nos. 3,837,354 and 5,311,910. It is further known to attach the end cap to the housing with screws, such as shown in U.S. Pat. No. 3,757,523, or by welding. In many of these techniques, however, it is apparent that the assembly and manufacturing steps are time-consuming and/or difficult, and it is believed that some accumulators have fatigue issues in certain higher-pressure applications, and hence have undesirably short operating lifetimes. Other of these techniques (such as welding) are faster, but can damage or degrade O-ring seals and rubber packing materials associated with the end caps, if not carefully monitored and controlled.
Thus, it is believed there is a demand in the industry for a new accumulator, and a new technique for retaining an end cap to a canister of an accumulator, which is relatively straightforward, and which maintains a permanent and fluid-tight attachment under operating pressures.
The present invention provides an improved accumulator for a fluid system, and a method for manufacturing such an accumulator, which is relatively straightforward in that it uses conventional forming machinery and has few steps, and maintains a permanent and fluid-tight attachment of the end cap(s) to the canister.
According to the present invention, the accumulator includes a canister and an end cap at one or both ends of the canister. Each end cap has a generally cylindrical peripheral surface, with a groove or channel having gradually tapered or curved walls, formed circumferentially around the peripheral surface of the cap, and spaced from the axial ends of the cap. An annular, radially-outward projecting flange or step is provided at the axially outer end of the cap, and serves as a locating feature for the cap when it is inserted into the canister. Once the cap is inserted into the canister and located via the flange, a forming tool such as a crimping machine is used to mechanically deform the canister into the groove. The rounded shape of the groove creates a permanent, fluid-tight seal with the canister.
The accumulator of the present invention can be used with either a piston or bladder, depending upon the particular application. The piston and bladder are preferably of a type generally known, and include an appropriate fluid-tight seal with the walls of the accumulator.
Thus, the present invention provides an improved accumulator, and method for manufacturing such an accumulator, which is relatively straightforward and maintains a firm and fluid-tight attachment of an end cap to the canister. Further features and advantages of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings.